Mike said:
...I replaced the fuel pump
assembly with another one which I got from a wrecking yard, and was told
that it was from a 1996.
The pump works fine, but the guage reads between E (when half full of gas)
and about 1/3, when full of gas. The float assembly moves ok on the
replacement unit. It just seems to me that the resistance range of the
sending unit is different than the old one I removed...
OK - here's what I think's going on: The fuel level sender is at its
lowest resistance when the tank is full - I don't know the specs. on
your van, but typically it would be on the order of 60 ohms (float full
up position). It goes to something on the order of 1000 ohms when the
tank is empty (float all the way down).
I think the wiper is slightly corroded (adding resistance into the
reading). This makes sense because:
(1) It has been sitting unused for a while (no wiping action to clean it
off) possibly in fuel, possibly in air, possibly in mixture of air and
moisture or fuel and water, and
(2) Higher resistance pushes the reading to towards empty (higher
resistance => lower gage reading). This would also have the effect of
compressing the gage scale downward (towards 'E'), which you are also
seeing.
Take it out, and carefully remove any covers from around the resitance
element and wiper. Very carefully clean both. Be careful - those wires
on the resistance element are very fine and delicate (meaning "easy to
break", in which case you throw it away). Try using some TV tuner
cleaner (Radio Shack).
To monitor your progress, read the resistance across the sensor (via the
two connector pins) at float full-up and full-down positions before you
start, and then as you clean it. I'm betting you will see the
resistance come down to the levels given above, and it will start
reading right.
Another type of problem that you see on sending units is broken
resistance element wires (they can completely wear thru from a lifetime
of cycling), but the behavior you are describing is not consistent with
that. I have no doubt that the wiper and/or resistance element wire
wiping surfaces are corroded - it fits the history of sitting in a junk
yards for an unknown period of time and the symptoms you have described.
I can't emphasize enough how delicate those wires are. You might try
just moving the float up and down a bunch of times (to wear thru the
corrosion) after squirting TV tuner cleaner (or electrical contact
cleaner) onto the resistance element and wiper without otherwise
directly contacting the element or wiper with your hands or any tools.
The other thing to watch out for when fooling with the wiper is
springing the wiper back a little so it doesn't make good contact with
the proper amount of pressure against the resistance wires - another
reason to avoid directly messing with it.
Let me know how it goes.
Sorry for the confusion earlier on in the thread - I confused Tom Ruta
with you when he posted.
Bill Putney
(to reply by e-mail, replace the last letter of the alphabet in my
address with "x")
